Guns, Guns, Guns and more Guns..... Yippee!!
The sheer number of weapons available and mod options to upgrade these weapons is frankly amazing. There is a sizeable number of different weapon types for each of the various categories: melee, unarmed, firearms, energy and heavy weapons, so you can choose to specialize your character in one or all of these disciplines.
Perhaps the only downside is that you will not be able to carry them all about, even with 2 NPCs accompanying you - that is if you intend to carry enough ammo with you. The other this is that there difference between each weapon is negligible. But thats down more to the engine as each weapon is wonderfully rendered and is instantly recognizable in your characters hands.
If you play Fallout NV for the combat this is definitely something you should consider. If you play more for the story, dialogue and adventure then its probably something you can do without. Unless you are a completist like me.
Worth the price though as it adds so much fun and variety to how you can kill your enemies.